How do we go about weighing a helicopter? And why do it?
Weight and Balance
Every time a helicopter is prepared for a flight, the pilot must conduct a weight and balance check. This procedure ensures then helicopter flies within the performance envelope of the manufacture for a safe flight
A helicopter always starts with a Basic Empty Weight, which is the weight of the helicopter itself, installed equipment, unusable fuel and operating fluids (eg. hydraulic fluid and oil). Then, you add the variable weight or Payload – ie. pilots, passengers, baggage, removable seats or other removable interior fittings, fuel, and operational fluids.
Combining the Basic Empty Weight and the Payload results in the Gross Weight.
To ensure a safe flight, the aircraft must operate within its Maximum and Minimum Gross Weights.
The position of a helicopter’s Centre of Gravity changes depending upon the loading. Therefore the weight distribution of the payload is very important to maintain a balanced flight.
The reference point for measuring loading positions is called a Datum. This imaginary line is model specific and established by the manufacturer.
Changes in the variable weights and loading positions result in the centre of gravity moving longitudinally (forward and aft) and laterally (left and right) of the Datum point.
It is important to note that these changes also happen during a flight, e.g. from fuel consumption. Therefore, to ensure a safe flight, the aircraft must continually operate within precise, allowable limits for centre of gravity called Envelopes.
Weighing a Helicopter
To complete future weight and balance calculations, there needs to be a starting weight. This is an accurate number reflecting the weight of the helicopter as built, outfitted and painted. Yes, paint adds weight! This is why we need to weigh the helicopter at the point of completion.
The equipment for weighing the helicopter is very sensitive. That being the case, the environment that the helicopter is weighed in needs to be one that will not influence the scales. For example a light wind can cause the main rotor blades of a helicopter on the ramp to flex. Loads are imposed and released, transferred to the scales, and as a result, you will see the weights fluctuate. So weigh the helicopter in a quiet environment, inside without any significant airflow around it.
The weighing process involves lifting the helicopter onto jacks that are placed below the four cross-tube skid corners of the landing gear. Male coupling points have been affixed to the landing gear that fit in to the receiving jacks. All of the jacks have designated colours and these are connected to a processing unit, which measures the mass from each jack. Finally, the loads are combined to represent a load condition for the whole helicopter.
[Technician preparing the weighing equipment. Note the different colour-coded cables and plugs.]
[Weighing jack underneath front right cross-tube skid corner of landing gear.]
The flexibility of helicopters like the H145 (Airbus) as both a VIP and “SUV” helicopter is based upon the ease in which the interior can be modified. So, what will the helicopter carry on every mission?
Any seats, items of cabinetry and other interior fittings that can be removed should be weighed separately to enable accurate weight and balance checks. This extends to the headsets, iPads for electronic flight bags, paperwork, and even bottled water. They all add weight.
Whenever the helicopter is modified it needs to be reweighed; even when changing the interior outfitting or updating the paint scheme! Knowing an accurate weight of the helicopter in any configuration predicates its mission effectiveness, the passengers it can carry, the amount of onboard luggage, and the range it can fly.
So, can it do the mission it was purchased for?
Weight and Balance in Practice
As we mentioned at the beginning of this editorial, weight and balance checks need to be conducted accurately before every flight to ensure a safe journey. However this is sometimes not as straightforward as it may seem.
This is because passenger loads will vary between men and women, large and small, children and adults, even pets – from a Yorkshire terrier to a St Bernard! Their clothes may be beach wear or full evening dress. Additionally, what travels with them extends beyond carry-on bags, to bicycles, giant chocolate birthday cakes, golf clubs, boxes of flowers, and ski gear. Yacht-embarked helicopters may bring provisions for the vessel. They may carry engineer spares. All these elements make up the payload, and you need to be able to weigh or accurately determine all of their weights.
All of these calculations used to be done by hand. But today’s technological world allows us to use software models, where the input of data calculates resultant weight and balance records for each specific flight leg. They give the pilot the assurance that they are not flying beyond the maximum gross weight for the helicopter, and that it will remain within the centre of gravity envelope that has been calculated for it. It is important to remember, staying within these limits will mean a safe flight; move outside this envelope and you enter a world that the helicopter has not been certified for.
Stay in the box, and enjoy the flight !
This is only a small part of the delivery process, and the wider Helicopter Lifecycle, read more about it 👉 here.
Or you can always get in touch directly to talk about it – details are on my 👉 contact page.
Are you looking for an operator for your newly weighed and delivered helicopter? Visit Luviair’s website 👉 here.